This invention relates to the control of an air conditioner used in a process of treating air in a compartment to regulate its temperature and, more particularly, to a method and apparatus for controlling an air conditioner of the type which can create air flows at different temperatures into the compartment. While the general principles and teachings hereinafter disclosed are applicable to all air conditioners, the invention is hereinafter described in detail in connection with its application to an air conditioner for use in automotive vehicles.
There has been developed air conditioners of the single-flow type having an air passage which terminates at its downstream end in a single mixing chamber opening into a compartment through defroster, vent and floor outlets. Each of these outlets is controlled to selectively block or permit air flow through it into the compartment in accordance with a selected air-blowing mode. The air passage contains an air cooling device and an air heating device located downstream of the air cooling device. A mixing door is located on one side of the air heating device to provide a bypass passage to divide air into two flows, the first being directed through the bypass passage into the mixing chamber. The second air flow is directed to the air heating device where it is heated and hence into the mixing chamber where it is mixed with the first air flow. With such a single-flow type air conditioner, however, it is impossible to blow air flows at different temperatures into the compartment or to meet the requirement of blowing air at relatively high temperature from the floor outlet while blowing air at relatively low temperature from the vent outlet.
A second type of air conditioner, which is referred to as dual-flow type air conditioner, has been developed to overcome such disadvantages attendant on single-flow type air conditioners. Such a dual-flow type air conditioner has an air passage which terminates at its downstream end in a chamber opening into a compartment through defroster, vent and floor outlets. The chamber is divided into two mixing chambers. The air passage contains an air cooling device and an air heating device located downstream of the air cooling device. Mixing doors are located on opposite sides of the air heating device to provide bypass passages to divide air into three flows, the first being directed through one bypass passage into the first mixing chamber. The second air flow is directed to the other bypass passage into the second mixing chamber. The third air flow is directed to the air heating device where it is heated and hence into the first and second mixing chambers. The temperatures of air in the first and second mixing chambers are controlled separately by independently adjusting the positions of the first and second mixing doors.
For dual-flow type air conditioners, the control of mixing door positions is required to decrease the temperature difference between compartment upper and lower portions as the ambient temperature increases since the compartment lower portion should be warmed to a higher temperature at relatively low ambient temperatures than at relatively high ambient temperatures whereas the temperature difference between the compartment upper portion and the atmosphere should be maintained in a small range. When the ambient temperature exceeds a value, however, such a dual-flow type air conditioner makes it difficult to effect such mixing-door-position control due to a small difference between target values for temperatures of the compartment upper and lower portions at high ambient temperatures and circulation of warmed air from the compartment lower portion to the compartment upper portions,. The difficulty of controlling the mixing door positions may be a cause of warmed air blowing into the compartment in a "vent" mode and of cooled air blowing toward a user's feet in a "bi-level" mode without an appropriate change between "vent" and "bi-level" modes.
Therefore, the present invention provides an improved method and apparatus for the control of a dual-flow type air conditioner which can provide an appropriate change of air-blowing mode and which can enhance passenger comfort.